One of the many problems with tutorials is that they either skip over the things the makers consider as so basic that they don't want to waste time explaining it, or they're made by people who poorly understand those basics themselves so they get it all wrong and don't even notice it themselves.
The advice you got from @groundFungus is good; if you do it that way, you'll have a robust setup that will actually keep working reliably once you get it up and running.
Be sure to choose a 12V supply that's sufficiently powerful for your motor (and all the rest) taking into account its stall current (not just the run current).